As the process of producing 2-cyano-4-oxo-4H-benzopyran compounds, for example, there has been known a process using 2-hydroxyacetophenone compounds as the starting material (see, e.g., Journal of Medicinal Chemistry, 1972, Vol. 15, No. 8, which is shown in the following reaction scheme: ##STR4##
In the above process, however, since an alcohol is used as the solvent in the second and third steps, and ammonia is used in the third step, serious problems will occur that a great amount of Waste water containing the alcohol of high concentration or containing ammonia has to be discharged in the production on an industrial scale.
In the fourth step, ordinary conditions for the dehydration of carboxamides are used; for example, (a) phosphorous oxychloride, phosphorous pentoxide or the like is used as the dehydrating agent and DMF, pyridine or a mixture thereof is used as the solvent; or (b) phosgene is used as the dehydrating agent and a hydrocarbon such as dichloromethane or dichloroethane is used as the solvent.
However, the conditions (a) has a disadvantage in that complicated procedures are necessary for the removal of the solvent from the waste water because DMF or pyridine used as the solvent is soluble in water and such a solvent gives a high load on the waste water. Also the conditions (b) are not always satisfactory for the production on an industrial scale because relatively high temperatures are required therefor.
In the above reaction scheme, it has been known that the following side reaction will be caused in the process (v) which is conducted by way of acid chlorides. ##STR5##
If the substituent R.sup.1 or R.sup.2 in the general formula (1) is a benzoylamino group substituted with an alkoxy group, there is required a step of reacting an acid halide of the general formula (12): ##STR6## wherein R.sup.5 is C.sub.1 -C.sub.20 alkyl or aralkyl and Z is halogen, with a compound of the general formula (13): ##STR7## wherein R.sup.1" is hydrogen, halogen, hydroxy, C.sub.1 -C.sub.5 alkoxy, nitro or amino, in the presence of a base.
In usual cases, pyridine or an aliphatic amine such as triethylamine is used as the base. If an aliphatic amine is used, there will occur a problem that a by-product may be formed by the additional acylation of the hydroxyl group of the compound (13). If pyridine is used, the above step is not always satisfactory for the production on an industrial scale because much difficulty is found in removing it from the waste water.